7.3.6.5.2 The narrative synthesis of data
The results of all systematic reviews require some degree of narrative. Where a meta-analysis has been performed, that narrative may focus on synthesis of the characteristics of studies and their quality to explain and interpret the calculated effect estimates. In instances where meta-analysis has not been possible, the review authors will have to resort to narrative synthesis of the results of the included studies also. Narrative synthesis relies primarily on the use of words and text (tables are often included also, see Section 2.8.3) to summarise and explain the findings of a synthesis process. Its form may vary from the simple recounting and description of study characteristics, context, quality, and findings. The textual description of studies (individual or group of studies) and the thematic analysis methods are briefly presented below. Further exploration as well as worked examples for these approaches is provided by Lucas & co (Lucas, Baird et al. 2007).
Textual descriptions of individual studies. Summaries of individual studies can be structured to provide details of the setting, participants, exposure, and outcomes, along with any other factors of interest (e.g. the income level of the users, age of users, previous experiences, attrition, length of follow-up, sample size);
Textual descriptions of groups of studies. Based on relevant criteria (e.g. types of participants) included studies can be sub-grouped. Subsequently, commentaries summarizing key aspects of the studies in relation to the sub-group within which they were included are produced. In a final step, the scope, differences and similarities among studies are used to draw conclusions across the studies.
Where a narrative synthesis is undertaken to describe the included studies and their conclusions, it is important to discern how the evidence was weighted and whether conclusions were biased. It is recommended that the characteristics of the studies and the data extracted are emphasised and tables, graphs, and other diagrams are made use of to compare data (Lockwood and White 2012). The narrative summary will present quantitative data extracted from individual studies, as well as, where available, point estimates (a value that represents a best estimate of effects) and interval estimates (an estimated range of effects, presented as a 95% confidence interval).
Because a potentially large amount of data can be conveyed in a narrative summary, consistency can be ensured in the results section if all reviewers agree beforehand on a structure for the reporting of results. If a structure is not followed, the report of results may appear incomplete or unreliable (Lockwood and White 2012). However, if included studies do not provide the relevant information to comply with a structure, it should be made clear in the summary. A textual combination of data is often used when the included studies are dissimilar in terms of patients, methods, or data.